QMOOD (Quality Model for Object-Oriented Design) is a software engineering model used to evaluate the quality of object-oriented software designs. QMOOD was developed by Dr. C.K. Chang and his colleagues at the University of Alabama in the late 1990s. The model is based on the premise that the quality of software is directly related to its design, and that certain design characteristics can be identified and measured to determine the overall quality of a software design.

The QMOOD model defines six design characteristics that are essential for high-quality object-oriented software designs. These characteristics are:

1. Modularity
2. Reusability
3. Extensibility
4. Understandability
5. Functionality
6. Effectiveness

Let’s take a closer look at each of these characteristics.

1. Modularity: Modularity refers to the degree to which a software design can be divided into smaller, independent modules. This allows for easier maintenance, testing, and reuse of code. In QMOOD, modularity is measured by the number of modules in the design and the average number of connections between them.
2. Reusability: Reusability refers to the degree to which a software design can be used in multiple contexts. This allows for greater efficiency in software development and reduces the need for redundant code. In QMOOD, reusability is measured by the number of reusable modules and the percentage of the design that is reusable.
3. Extensibility: Extensibility refers to the degree to which a software design can be extended or modified to accommodate new requirements or features. This allows for greater flexibility in software development and reduces the need for redesign. In QMOOD, extensibility is measured by the number of extension points in the design and the average number of connections between them.
4. Understandability: Understandability refers to the degree to which a software design is easy to understand and maintain. This allows for greater efficiency in software development and reduces the risk of errors. In QMOOD, understandability is measured by the number of comments in the code and the ratio of comments to lines of code.
5. Functionality: Functionality refers to the degree to which a software design meets its intended functional requirements. This allows for greater efficiency and effectiveness in software development. In QMOOD, functionality is measured by the number of functions or methods in the design and the complexity of those functions.
6. Effectiveness: Effectiveness refers to the degree to which a software design meets its intended non-functional requirements, such as performance, security, and reliability. This allows for greater efficiency and effectiveness in software development. In QMOOD, effectiveness is measured by the number of non-functional requirements specified for the design and the degree to which those requirements are met.

QMOOD has been used in a number of studies to evaluate the quality of object-oriented software designs. For example, in a study conducted by Dr. Chang and his colleagues, QMOOD was used to evaluate the quality of two different software designs for an e-commerce system. The first design was found to be of higher quality than the second design based on the QMOOD metrics.

Another study used QMOOD to evaluate the quality of several open-source software projects. The study found that the projects with higher QMOOD scores had fewer defects and were easier to maintain than those with lower QMOOD scores.

In conclusion, QMOOD is a valuable tool for evaluating the quality of object-oriented software designs. By measuring the six essential design characteristics of modularity, reusability, extensibility, understandability, functionality, and effectiveness, QMOOD provides a comprehensive view of the quality of a software design. By using QMOOD, software developers and engineers can identify areas for improvement and create high-quality object-oriented software designs that are easier to maintain, test, and reuse, ultimately leading to more efficient and effective software development.